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題名 | 建立高精確度鈾和釷同位素固態熱離子源質譜儀測量術:初步評估=High Precision U and Th Isotopic Measurement Using Thermal Ionization Mass Spectrometry: A Preliminary Evaluation |
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作 者 | 游鎮烽; | 書刊名 | 成功大學學報 |
卷期 | 35(科技.醫學篇) 民89.11 |
頁次 | 頁1-10 |
分類號 | 449.6 |
關鍵詞 | 鈾和釷同位素; 放射性定年; TRU樹脂; U and Th isotopes; Radiometric dating; TRU resins; |
語文 | 中文(Chinese) |
中文摘要 | 放射性定年法是地球科學發展史上重大的研究課題之一。尤其是對第四紀以來地球表面環境變化的探討,適當定年工具極其缺乏;碳-14(半衰期約5700年)定年法,雖可用於量測最近5萬年內標本,但其應用範圍嚴重受限於所需材料的特性。鈾-釷不平衡系是唯一可以延伸應用至近60萬年樣品的準確定年法;但是傳統上使用的放射化學法,卻受制於計數器精確度和所需樣品量大小;新型改良的熱離子源鈾-釷質譜術,不但可改進精確度達10倍以上,減低標本量為1/10至1/100;同時更可減少計數時間,提高研究效率。此質譜術可拓展應用於低濃度、小樣品(如有孔蟲、牙齒、骨骼、微量孔隙水及碳酸鈣等)或需高解析度之標本(如珊瑚或鐘乳石)。 本研究利用一系列同位素標準溶液(包括NBS 987、NBS 951、L-SVEC及標準海水等),針對成功大學地球科學系MAT262型質譜儀,進行離子計數器的線性分析及豐藏度測試;另外也利用國際黑曜石標準樣品(A-THO),建立TRUSPEC樹脂的鈾和釷化學分離步驟;並標定鈾-233、鈾-236及釷-229標準溶液的準確鈾或釷濃度,且應用於分析自然樣本及測定實驗室蒸餾水、各種酸鹼溶液、樹脂及化學流程中之可能鈾和釷本體值。 |
英文摘要 | Radiometric dating has become one of the most fundamental tools in Earth Sciences studies. There are, however, only few techniques available for determining the age of geological samples in Holocene. The 14 C method has been used extensively for carbonaceous materials including organic carbon, charcoal, or skeleton younger than 50,000 years. The 234U-230 Th method is the only other precise technique can be applied todate samples up to 600,000 years. The traditional 234U-230 Th radio chemical technique, however, was limited to its analytical precision and the amount of material needed. The newly developed 234U-230 Th technique using thermal ionization mass spectrometry (TIMS) can improve the analytical precision about 10 times, reduce the sample size to 1/10 ~ 1/100, and savethe machine time to hours. This technique is particularly suitable forsamples with low U and Th concentration, small size (e.g., foramini feraltests, mammoth teeth or skeleton, pore waters or carbonates), or other high resolution needed projects (e.g., corals or speleothems for environmentalstudies). In this study, I have examined carefully the MAT262 masss pectrometer at the Department of Earth Sciences, National Cheng'Kung University using a series of isotopic standards, including NBS 987, NBS951, L-SVEC and seawater standards to cross-checking the abundance sensitivity near U and TH mass ranges and the Daly-Faraday linearity. Additionally the International Obsidian Standards (A-THO) were used to calibrate the TRUSPEC column procedures for efficient separation of U and Th from other matrix, as well as to standardize the prepared 233U , 236U and 229 Th spike solutions. A mixed 233U-236U-229 TH spike solution was calibrated against the A-THO standard for U and Th concentration and isotopic compositions. Any potential U and Th contamination from acids,chemicals, resins or waters was evaluated carefully. |
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